I know I've read and seen that the earlier M&P's slides were stamped Stainless on the left hand side but what I would liked to know (if any of you experts know) is when did S&W STOP stamping the slides on the M&P line? My M&P.40FS serial # DYB5xxx was assembled and test fired on Friday 27 Jul 2012 and it is not stamped stainless. Thanks All
Later & Keep your Powder Dry!

I believe they started phasing out the stamp in May-June of 2011. By December 2011 they were all being made with out the stamp. Smith and Wesson CS said that all of the literature and advertising already said that they were stainless and they felt that stamping the slide was no longer needed.

It helps me when I purchase them on the used market. If there is no stamp I know they are less then a year to year and a half old. The blue box also helps date them as newer or older.
Hope this helps